1. Field of the Invention
The present invention relates to a structure formed on a sprocket to aid in shifting of a bicycle chain.
2. Description of the Related Art
In a multi-stage sprocket assembly of a bicycle having a derailleur, a chain is movable by a shifting force of the derailleur from a small sprocket to a large sprocket. In a conventional sprocket assembly, a side surface of the chain contacts a side surface of the large sprocket, and the chain is supported by the large sprocket through a frictional force produced by the contact. With rotation of the large sprocket, the chain is raised radially outwardly of this sprocket to engage teeth of the sprocket.
However, shifting of the chain in this manner requires a sufficient frictional force produced between the chain and the large sprocket to pick up the chain reliably with rotation of the sprocket. In other words, the derailleur must exert a strong force to press the chain upon the large sprocket.
When a heavy drive load occurs during a shifting operation, the chain may slip from the large sprocket. This makes it very difficult to pick up the chain with the large sprocket, or results in a delay of chain shift.